The idea that social breakdown in a neighbourhood can increase the risk that some residents will develop schizophrenia may not come as too much of a surprise, but the notion that too much social cohesion might also be a risk factor, probably will.

James Kirkbride and colleagues sent questionnaires to over 16,000 people in South London to obtain their views on the social cohesion of their neighbourhoods. For example, participants answered questions about how much graffiti was in their area, how many thefts there were and whether someone was likely to help their neighbours. Just over 4000 people replied.

The data on neighbourhood social cohesion was then compared with new diagnoses of schizophrenia made in those areas over a period of twenty-four months, as recorded several years earlier by a separate study.

The researchers found that neighbourhoods with either below or above average social cohesion, tended to have had more new incidences of schizophrenia, even after taking into account differences between neighbourhoods in the age, gender and ethnicity of the local populations.

The harmful effect of low social cohesion is easier to explain: in socially fragmented neighbourhoods, people at risk of schizophrenia are less likely to receive the support they need to prevent them from developing psychosis. But what about the harmful effect of too much social cohesion? The researchers speculated that it’s likely “some residents in neighbourhoods measured as having ‘high’ social capital were excluded from access to that social capital, conversely increasing their risk of schizophrenia.” Another possibility is that schizophrenia is more likely to be detected in more socially cohesive neighbourhoods.

Incidentally, although this study design can’t prove that neighbourhood social cohesion directly causes changes in rates of schizophrenia, the researchers said it’s unlikely that the causal relationship runs in the opposite direction, simply because absolute rates of schizophrenia are so low._________________________________